Demon: Mot
Requirements: Plugin: Majestic Blaze or Plugin: Dark Orb of the Inferno
Once you start Act 16 you will be sent to the town you did not visit during Act 13 and trigger a boss fight with the opposite boss (in other words, if you fought Uriel in Act 13, you'll fight Surt in Act 16, and viceversa).
Regardless of the Act you face each in, the questions will always be the same, so reply correctly according to the answers below and you will obtain the Mot Plugin: Gates of Hades once you talk to Yamamoto to continue your act.
SURT
For Freedom
* Accept Freedom dictated by Demons
* Yes - Take side with the Demons
* Yes - Stand against Gods
URIEL
For Peace
* Yes - Cooperate with the Savior
* Yes - Freedom is without order
* Yes - Pledge to fight for Millennial Kingdom